1. Field of the Invention
This invention relates generally to chemical mechanical planarization apparatuses, and more particularly to methods and apparatuses for optimizing chemical mechanical planarization applications by optimizing the controllability of a fluid bearing generated by a platen.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then, metal CMP operations are performed to remove excess material.
A chemical mechanical planarization (CMP) system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, a rotary polishing pad, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material or polyurethane in conjunction with other materials such as, for example a stainless steel belt. In operation, the belt pad is put in motion and then a slurry material is applied and spread over the surface of the belt pad. Once the belt pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the belt pad. In this manner, wafer surface is planarized substantially. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A shows a linear polishing apparatus 10 which is typically utilized in a CMP system. The linear polishing apparatus 10 polishes away materials on a surface of a semiconductor wafer 16. The material being removed may be a substrate material of the wafer 16 or one or more layers formed on the wafer 16. Such a layer typically includes one or more of any type of material formed or present during a CMP process such as, for example, dielectric materials, silicon nitride, metals (e.g., aluminum and copper), metal alloys, semiconductor materials, etc. Typically, CMP may be utilized to polish the one or more of the layers on the wafer 16 to planarize a surface layer of the wafer 16. The linear polishing apparatus 10 utilizes a polishing belt 12, which moves linearly in respect to the surface of the wafer 16. The belt 12 is a continuous belt rotating about rollers (or spindles) 20. A motor typically drives the rollers so that the rotational motion of the rollers 20 causes the polishing belt 12 to be driven in a linear motion 22 with respect to the wafer 16.
A wafer carrier 18 holds the wafer 16. The wafer 16 is typically held in position by mechanical retaining ring and/or by vacuum. The wafer carrier positions the wafer atop the polishing belt 12 so that the surface of the wafer 16 comes in contact with a polishing surface of the polishing belt 12.
FIG. 1B shows a side view of the linear polishing apparatus 10. As discussed above in reference to FIG. 1A, the wafer carrier 18 holds the wafer 16 in position over the polishing belt 12 while applying pressure to the polishing belt. The polishing belt 12 is a continuous belt typically made up of a polymer material such as, for example, the IC 1000 made by Rodel, Inc. layered upon a supporting layer. The polishing belt 12 is rotated by the rollers 20 which drives the polishing belt in the linear motion 22 with respect to the wafer 16. In one example, a fluid bearing platen 24 supports a section of the polishing belt under the region where the wafer 16 is applied. The platen 24 can then be used to apply fluid against the under surface of the supporting layer. The applied fluid thus forms a fluid bearing that creates a fluid pressure on the underside of the polishing belt 12 which is applied against the surface of the wafer 16. Additionally, typical platen designs tend to use a significant amount of fluid to produce a fluid bearing between the platen 24 and the polishing pad 12. In one example, high flow regulators are utilized to input air through the platen 24. Unfortunately, by use of a high flow regulator, large amounts of air are utilized during a CMP operation. Large usage of fluid can lead to increased wafer production cost and therefore is generally undesirable. Generally, uniformity is desired where the material removal rate is evenly distributed across the entire contact surface that interfaces with the wafer so the wafer surface becomes substantially planar. This typically requires control of polishing pressure applied by the fluid bearing. But, there can be times where polishing pressure in different regions of the wafer is desired to be varied such as times when oxide deposition on the wafer has a distinctive thickness profile as discussed below in reference to FIGS. 1C and 1D.
FIG. 1C shows a graph 30 illustrating a profile of non-uniform oxide deposition on a wafer. In this example, the oxide layer that has been deposited is thicker in the center and the edge of the wafer and thinner in the area between the center and the edge. This can occur due to equipment optimization limitations. Therefore, when platens that apply uniform polishing pressure across the wafer are utilized resulting in a uniform removal rate, the original non-uniformity from the deposition is preserved after planarization. Thus, when, for example, the oxide layer that has been applied is thicker in the center and the edge and thinner in the areas in between, this may result in too little polishing in the edge and center portions of the wafer and too much polishing in the other regions of the wafer. Unfortunately, because prior art platens are configured to only outputs fluids from outlets, wafer polishing profiles typically cannot be managed to match many wafer thickness profiles.
FIG. 1D shows a graph 40 of another exemplary profile of an non-uniform oxide layer that has been deposited on the wafer. In this example, if a wafer that is thicker in the edge and thinner in the middle is polished, the polishing can result in too much removal of oxide in the center region while too little removal takes place in the edge regions of the wafer. Therefore, the wafer with the thickness profile as shown in graph 40 may not polished to a substantially planar surface.
As shown by FIGS. 1C and 1D, there are numerous types of wafer thickness profiles that can occur with different oxide deposition equipment from different manufacturers. Therefore, wafer polishing equipment attempting to apply uniform polishing pressure across the wafer is not able to adjust polishing pressures throughout the various portions of the wafer. Such resultant non-uniform wafer thicknesses may be undesired and can be detrimental to efficient wafer processing operations.
In view of the foregoing, there is a need for an apparatus that overcomes the problems of the prior art by having a platen that can effectively control different polishing pressure profiles during CMP operations.
Broadly speaking, embodiments of the present invention fill these needs by providing a platen that enables management and control of polishing pressure in different parts of the wafer during a CMP process by having the ability to increase or decrease fluid pressure in different areas over the platen. The platen may do this by having fluid outlets and fluid inlets to output and input air flow. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a platen is provided for use in a chemical mechanical planarization (CMP) system. The platen includes at least one fluid output zone having a plurality of fluid outlets, the at least one fluid output zone being disposed below a polishing pad and being capable of providing fluid pressure to the polishing pad. The platen also includes at least one fluid input zone having a plurality of fluid inlets, the at least one fluid input zone being disposed below the polishing pad and being capable of removing the fluid pressure. The platen is capable of managing fluid pressure applied to the polishing pad to achieve a particular polishing profile during a CMP operation.
In another embodiment, a method for wafer planarization using a linear chemical mechanical planarization (CMP) system is provided. The CMP system has a platen with at least one fluid input zone and at least one fluid output zone disposed below a polishing pad. The method includes outputting fluid from at least one fluid output zone to an underside of the polishing pad to increase fluid pressure on the polishing pad. The method further includes inputting fluid into at least one fluid input zone to decrease the fluid pressure on the polishing pad. The increasing of the fluid pressure on the polishing pad increases polishing pressure on a wafer and the decreasing of the fluid pressure on the polishing pad decreases polishing pressure on the wafer. Each of the at least one fluid output zone and each of the at least one fluid input zone are capable of being managed to achieve a particular polishing profile.
In yet another embodiment, a platen is provided which includes a surface capable of supporting a portion of a polishing pad. The platen also includes a plurality of outlets located throughout the surface, each of the plurality of outlets being capable of outputting a fluid toward an underside of the polishing pad. The platen further includes a plurality of inlets located throughout the surface, each of the plurality of inlets being capable of removing the fluid away from the underside of the polishing pad.
Because of the advantageous effects of increasing and decreasing controlled pressure to and from various areas of the wafer, embodiments of the present invention provide significant improvement in planarization and control over polishing profiles. Specifically, the platen described herein includes both at least one fluid out region and at least one fluid input region. In addition, embodiments of the platen utilize less fluid output zones thereby using less fluid than prior art platens while still enabling the optimization of polishing profiles. Consequently, the platen may not only control polishing in various portions of the wafer, but in addition, the platen may use significantly less fluid than prior art platens. Therefore, the platen described herein increases wafer production efficiency and decreases wafer production costs. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.